This disclosure relates generally to turbomachines, and more particularly to both gas turbines and steam turbines, and the design of turbine blade composed of inserts made from different materials.
Steam turbines include, but are not limited, to steam turbine power generation equipment and shipboard steam turbine propulsion equipment. An exemplary steam turbine typically contains a high-pressure turbine section, a low-pressure turbine section, or a combination of both, which is rotated by the steam flow. Gas turbines include, but are not limited to, gas turbine power generation equipment and gas turbine aircraft engines. An exemplary gas turbine typically includes a core engine, having a high pressure compressor to compress the air flow entering the core engine, a combustor in which a mixture of fuel and the compressed air is burned to generate a propulsive gas flow, and a high pressure turbine which is rotated by the propulsive gas flow and which is connected by a larger diameter shaft to drive the high pressure compressor. A typical front fan gas turbine aircraft engine adds a low pressure turbine (located aft of the high pressure turbine) connected by a smaller diameter coaxial shaft to drive the front fan (located forward of the high pressure compressor) and to drive an optional low pressure compressor (located between the front fan and the high pressure compressor). The low-pressure compressor sometimes is called a booster compressor or simply a booster.
In the exemplary steam turbine, typically the high and low pressure turbine sections have steam turbine blades each including an airfoil portion attached to a shank portion. In the exemplary gas turbine, typically the fan and the high and low pressure compressors and turbines have gas turbine blades each including an airfoil portion attached to a shank portion. Rotor blades are gas or steam turbine blades attached to a rotating gas or steam turbine rotor discs, respectively. Stator vanes are gas turbine blades or steam turbine blades attached to a non-rotating gas or steam turbine stator casings, respectively. Typically, there are alternating circumferential rows of radially-outwardly extending rotor blades and radially-inwardly extending stator vanes. When present in the gas turbine configuration, a first and/or last row of stator vanes (also called inlet and outlet guide vanes) may have their radially-inward ends also attached to a non-rotating gas turbine stator casing. Counter rotating “stator” vanes are also known in gas turbine designs. Conventional gas and steam turbine blade designs typically have airfoil portions that are made entirely of metal, such as titanium, or are made entirely of a composite. The all-metal blades, including costly wide-chord hollow blades, are heavier in weight, resulting in lower fuel performance and requiring sturdier blade attachments.
In a gas turbine aircraft application, the lighter all-composite blades, without a metal leading edge, are more susceptible to damage from bird ingestion events. Known hybrid blades include a composite blade whose leading edge is protected by metal (with the rest of the blade covered by a non-metallic coating) for erosion and bird impact reasons. The gas turbine fan blades typically are the largest (and therefore the heaviest) blades in a gas turbine aircraft engine and the front fan blades are the first to be impacted by a bird strike. Composite blades have typically been used in applications where weight is a major concern. However, the desire for reduced collateral damage during blade loss events in addition to higher operating speeds has created the desire to reduce the weight of these blades even further.
Prior attempts to overcome this problem have utilized composite sandwich airfoil construction including an airfoil portion comprised of a single composite low density insert core sandwiched between carbon/epoxy face sheets. While resulting in a lightweight design, stress states resulting from these single lightweight insert structures has shown to be problematic under bird strike conditions due to geometric stress concentration and modulus mismatch. More particularly, use of a single insert proved to produce inter-laminar stresses in excess of the composite material capability under static bird strike testing. Subsequent optimization of the single insert shape and size suggested that a solution was unobtainable.
Accordingly, there is a need for an improved turbine blade specifically, what is needed is a gas turbine blade, and especially a gas turbine fan blade, that is lighter in weight than either traditional composite or hybrid blade and including reduced geometric stress concentrations. What is also needed is a steam turbine blade that is lighter than either traditional composite or hybrid blades.